Previous studies have attempted to correlate hen production performance with diet. Lee et al. (Korean J Anim Sci 27(3):161-168 and 169-175, 1985) identify the energy and protein requirements of broiler breeder hens between 24 and 64 weeks of age. Although these optimum diets increased egg production at certain age stages, no increase in hatchability was seen with diets having optimum energy or protein levels. Similar studies by Lilburn et al. (Poul Sci 69(7):1126-1132, 1990) and Waldroup et al. (Poul Sci 55(6):2342-2347, 1976) also fail to report an effect of diet on hatchability.
Carnitine in poultry diet has been shown to have no effect on feed intake, body and abdominal fat weight or on carcass or liver lipid levels (Cartwright, Poul Sci 65(Suppl. 1) :21, 1986). Dietary carnitine has been shown to retard ethanol metabolism in broilers (Smith et al., Poul Sci 71 (Suppl. 1 ): 64, 1992). However, neither of these reports discuss an effect on the hatchability of the eggs laid by hen on such a diet.
Carnitine was found not suitable as a substitute for choline in the diet of quail (Chang et al., Poul Sci 94(5):1718-1720, 1975). In a control experiment of this study, carnitine was used as an additive to a standard diet containing choline. The added carnitine decreased the hatchability of the quail eggs. This observed decrease could be due to one or both of the following differences between this experiment and the present invention. Chang et al. used racemic carnitine (a mixture of both the D- and L- isomers), where L-carnitine is presently preferred. More importantly, the carnitine concentration was more than twice the upper concentration limit recommended by the present disclosure, i.e. 1400 mg/kg vs. about 675 mg/kg. As discussed below, the present inventors believe that there is an upper concentration limit for effectiveness.
Several patents have been issued which provide methods of increasing the hatchability of eggs. U.S. Pat. No. 2,734,482, issued to Seltzer involves distribution inside the egg of sex hormone, such as estrogens or androgens, through the wetting the outside of the egg shell with a liquid formulation of the hormone. Such treatment is said to improve the hatchability and viability of the resulting chicks. U.S. Pat. No. 4,604,968, issued to Christensen, discloses an increase in hatchability through the injection of eggs with a substance which increases the endogenous thyroid output of the developing embryo. U.S. Pat. No. 4,973,595, issued to Robel, discusses the increase in hatchability of turkey eggs by injecting pyridoxine at a particular developmental stage.
All of these patented methods involve treatment cf the eggs themselves, and thus are labor intensive and would involve major alterations in handling of the laid eggs. Therefore, there remains a need in the art for a method of increasing hatchability of the eggs which can be easily incorporated into existing farming techniques.
Accordingly, one aspect of the present invention is a diet for breeder hens which comprises an effective amount of carnitine, where the desired effect is an increase in the hatching percentage of eggs laid by the hens.
A further aspect of the present invention is a method of improving hatchability of eggs which involves feeding hens a standard diet which has been supplemented with an effective amount of carnitine.